It has heretofore been widely conducted as packaging and processing techniques for food products such as meat, ham and sausage, and other products to form a heat shrinkable multilayer film into a bag or pouch by a bag making machine and then fill contents thereinto, or subject contents directly or contents placed on a tray to automatic packaging while forming a bag. A variety of characteristics or properties is required for such packaging films, and the films are required to be well balanced among various characteristics or properties, for example, heat shrinkability, strength, heat resistance, high-temperature creep resistance, moldability, suitability for various packages, gas barrier properties, water vapor barrier properties and transparency.
For example, Japanese Patent Application Laid-Open No. 2002-172746 (Document 1) discloses a heat shrinkable multilayer film comprising at least three layers of an outer surface layer (a) formed of a thermoplastic resin, an intermediate layer (b) formed of a polyamide resin and an inner surface layer (c) formed of a sealable resin as a film satisfying these various characteristics. The thermoplastic resin forming the outer surface layer (a) is a polyester resin or polyolefin resin. The polyamide resin forming the intermediate layer (b) is a mixture of 60 to 85% by weight of an aliphatic polyamide resin and 15 to 40% by weight of an aromatic copolymer polyamide resin that is a copolymer of aliphatic diamine/isophthalic acid and aliphatic diamine/terephthalic acid. The sealable resin forming the inner surface layer (c) is essentially a copolymer having a density of less than 0.915 and composed of ethylene and an α-olefin. The heat shrinkable multilayer film is heat-treated after biaxial stretching treatment, and the shrink of the heat shrinkable multilayer film in water at 80° C. is 30% or higher in each of machine and transverse directions and 35% or higher in at least one direction of the machine and transverse directions. Document 1 describes a heat shrinkable multilayer film using a nylon 6-66 copolymer with a melting point of about 195° C. as the above aliphatic polyamide resin.
However, the heat shrinkable multilayer film described in Document 1 is still insufficient in heat resistance and high-temperature creep resistance though the film is sufficient in heat shrinkability, tensile strength, moldability, suitability for various packages, gas barrier properties, water vapor barrier properties and optical property.